The uncapped 20-year-old suffered ankle ligament damage during the Dragons' Heineken Cup defeat against Glasgow two days ago and he has now been replaced by the Scarlets' Rob McCusker as Wales prepare for their tournament opener against England on February 4.

Faletau is expected to be sidelined for up to six weeks after undergoing a scan and Wales physiotherapist Mark Davies said: "Toby has ligament damage to his ankle and will be in a boot for a period of two to three weeks. He will then begin rehab, meaning he is ruled out for around six weeks."

McCusker has won three caps, appearing as a substitute against South Africa at the Millennium Stadium last summer, before featuring off the bench in both Tests against New Zealand, also last June.

McCusker is more of a like-for-like replacement for Faletau than 98 times-capped openside Martyn Williams, who was the shock omission from Gatland's Six Nations squad.